Treat facebook as public information and don't put anything stupid on there. Thats all.
I just went to my first incoming students events this past weekend and I can say that people were very honest about the amount of facebook stalking of other students they had been doing. But it does seem useful for finding roommates keeping in touch with the people you meet at these events, etc. I say that as long as you don't have anything stupid up these I wouldn't worry.
Interesting BBC article titled "Social sites reveal class divide"Essentially, facebook is for college-bound, myspace is for high schoolers.http://news.bbc.co.uk/2/hi/technology/6236628.stm